Flasher circuit with outage indication

ABSTRACT

A flasher circuit has a power transistor controlling a circuit with a load therein; a multivibrator produces a timed pulse signal to the power transistor for turning the power transistor &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39;; and an additional transistor sensitive to the occurrence of an increased voltage drop across the load due to an outage is connected to the multivibrator for changing the time rate of the timed pulse signal.

United States Patent 91 Bolinger et al.

FLASHER CIRCUIT WITH OUTAGE INDICATION lnventors: John F. Bolinger; Wilhelm K. Kolster, deceased, both of Michigan City, Ind. by Christel E. Kolster, executrix Assignee: Meridian Industries, Inc., Southfield, Mich.

Filed: Mar. 23, 1972 Appl. No.: 237,569

Related US. Application Data Continuation of Ser. No. 40,288, May 25, 1970, abandoned.

US. Cl ..315/200 A, 315/130, 315/201,

340/81 R Int. Cl. ..H03b 3/282, H051) 39/09 Field of Search ..315/200 A, 130, 201;

[ May 22,1973

[56] References Cited UNITED STATES PATENTS 3,263,119 7/1966 Scholl ..340/8l 3,329,868 7/l967 Domann et a]. ..3 15/200 A Primary ExaminerJohn Kominski AttorneyGerald E. McGlynn, Jr. et al.

[57] ABSTRACT A flasher circuit has a power transistor controlling a circuit with a load therein; a multivibrator produces a timed pulse signal to the power transistor for turning the power transistor on; and an additional transistor sensitive to the occurrence of an increased voltage drop across the load clue to an outage is connected to the multivibrator for changing the time rate of the timed pulse signal.

6 Claims, 4 Drawing Figures Patented May22, 1973 3,735,196

- g 4 mzmgc mszzzizomr x2 M 20/ ATTORNEYS FLASIIER CIRCUIT WITH OUTAGE INDICATION This is a continuation of application Ser. No. 40,288, filed May 25, 1970 now abandoned.

BACKGROUND OF THE INVENTION I-leretofore various circuits have been proposed for use as flasher circuits. However, such flasher circuits have been, and often still are, susceptible to the occurrence of a particular lamp or bulb, within the overall load, becoming burned out. Such occurrences can become dangerous where, for example, the flasher circuit is employed as a directional turn indicator on motor vehicles or an emergency flashing system as on school buses or the like, because the vehicle operator may not have knowledge that a particular lamp or bulb is burned out and is assuming that all pedestrians as well as other vehicles are aware that he is signaling his particular intent to perform a particular vehicular maneuver.

Accordingly, the invention as herein disclosed and described is directly concerned with the solution of the above as well as other related problems.

SUMMARY OF THE INVENTION According to the invention, a switching circuit comprises electrical load means, a load circuit containing said electrical load means, first load switching means in circuit with said load circuit, second means for producing a cyclic control signal for causing said first means to be at times rendered conductive, and additional means responsive to the occurrence of an outage condition in said load means and being effective in response thereto to vary the cycle time of said cyclic control signal.

Various general and specific objects and advantages of the invention will become apparent when reference is made to the following detailed description considered in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS In the drawings, wherein certain details may be omitted, for purposes of clarity, from one or more views:

FIG. 1 is a schematic wiring diagram of a flasher circuit employing the invention disclosed herein;

FIG. 2 illustrates, in comparison, two graphs depicting two different modes of operation of the circuitry of FIG. 1; and

FIGS. 3 and 4 are fragmentary schematic wiring diagrams illustrating modifications of the invention shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in greater detail to the drawings, FIG. 1 illustrates a flasher circuit with outage indication means as comprising conductors l and 12 having their respective ends 14 and 16 adapted for connection to a suitable source of electrical potential 18 and ground as at 20. A first transistor 22 has its collector electrode 24 connected in series with a resistor 26 and conductor 12 while its emitter electrode 28 is connected to conductor 10. Similarly, a second transistor 30 has its collector electrode 32 connected, in series with a resistor 34, to conductor 12 while its emitter electrode 36 is connected via conductor 38 to the base terminal 40 of a load or power switching transistor 42 which, in turn, has its emitter 44 connected to conductor by means of conductor 45 and its collector terminal 46 connected via conductor 48 to electrical load 50. The other side of load 50 is connected to conductor 12 by means of a conductor 52.

Accordingly, for purposes of discussion, conductors 45, 48 and 52 may be considered as comprising a load circuit within which the power transistor 40 and load 50 are situated. Further, for purposes of clarity and ease of description, the load 50 is shown as comprising a plurality of loads 54, 56 and 58 arranged in parallel. Such loads 54, 56 and 58 may be thought of as comprising a plurality of flasher lamps carried as by an automotive vehicle or even, for example, a school bus.

Base electrode 60 of transistor 22 is electrically connected, via conductor 62, in series with a resistor 64 -which has its other end connected to conductor 12 while base terminal 66 of transistor 30 is connected to conductor 12 by means of a conductor 68 and resistor 70.

A first capacitor 72 has one side connected to a point electrically between resistor 26 and collector terminal 24 of transistor 22 while its other side is connected to conductor 68 as at 74. Somewhat similarly, a second capacitor 76 has one side connected to a point electrically between resistor 34 and collector electrode 32 of transistor 30 while its other side is connected to conductor 62 as at a point 78.

A fourth transistor 80 has its emitter 82 connected to conductor 12, as by conductor portion 84, while its collector 86 is connected to a resistor 88 which, in turn, is connected to point 74 as by a conductor 90. The base terminal 92 of transistor 80 is connected, via conductor 94, to conductor 48 as at a point 96. A resistor 98 is connected at its opposite ends to conductors 10 and 94 so as to be in parallel to power transistor 42.

It can be seen that each of transistors 28, 30 and 42 are of the P-N-P type while transistor 80 is of the N-P-N type. Generally, in the P-N-P type conduction therethrough will occur when the emitter is made sufficiently positive with respect to the collector and base while in the N-P-N type conduction therethrough will occur when the emitter is made sufficiently negative with respect to the collector and base.

OPERATION OF THE INVENTION Generally, transistors 22 and 30 comprise a multivibrator the operation of which is generally as follows. Let it now be assumed that a related control switch 100 has been closed and that transistor 22 has just switched on, creating current flow through the emittercollector circuit 28, 24 and that transistor 30 has switched off" or its non-conducting state.

At the instant that transistor 22 so switches on, capacitor 72 would have been fully charged so that the side thereof connected to point 74 is positive with respect to the other side of capacitor 72 which is connected between resistor 26 and collector 24. At this same time capacitor 76 will be in a discharged state.

Capacitor 72 now starts charging toward the opposite polarity by virtue of being essentially connected to 10 when transistor 22 is conducting and the emittercollector circuit 28, 24, thereof is completed. It can also be seen that because of the charge that existed on capacitor 72 at the instant that transistor 22 went into conduction and its connection to base electrode 66 of transistor 30, via conductor 68, the emitter-base circuit 36, 66, of transistor 30 are reverse biased (the base 66 being positive with respect to emitter 38) thereby keeping transistor 30 in an of or non-conductive state.

At this same time, capacitor 76 will start to charge essentially through the emitter-base circuit 28, 60, of transistor 22, and resistor 34. Such charging current of capacitor 76 holds transistor 22 conductive or hard on; further, even when charging of capacitor 76 is completed, transistor 22 will remain conductive by virtue of the base current provided through resistor 64.

As the potential across capacitor 72, holding transistor 30 off, is reduced, a condition is finally attained where the capacitor 72 voltage can no longer maintain transistor 30 in the non-conductive state. As transistor 30 starts to become conductive, by virtue of a biasing current through resistor 70, the collector to emitter voltage thereof drops and the now charged capacitor 76 starts to discharge, resulting in a reverse bias driving transistor 22 into non-conduction. When transistor 22 is thusly driven into non-conduction, the voltage across its emitter 28 and collector 24 increases causing capacitor 72 to again start charging through the emitter-base circuit of conductive transistor 30.

At the instant that transistor 30 became conductive, capacitor 76 was charged so as to have its side connected to point 78 positive relative to its side connected between collector 32 and resistor 34. However, as transistor 30 becomes conductive, capacitor 76 starts to charge toward the opposite polarity by virtue of the emitter-collector circuit 36, 32 being conductive and because of the current flow through resistor 64. As described with reference to capacitor 72, so now capacitor 76 produces a reverse bias on transistor 22 holding it in a non-conductive or off state.

During the time that transistor 30 is conducting, capacitor 72 is being charged so that its side connected to a resistor 70 will be positive with respect to the side thereof connected between collector 24 and resistor 26. Such charging of capacitor 72 is the consequence of the base current from transistor 30 which also serves to hold the transistor 30 in its on or conductive state. Transistor 30 is also maintained conductive for some period after capacitor 72 has been fully charged because of the base bias provided by resistor 70.

However, as capacitor 76 continues to discharge and the voltage thereacross approaches zero, the voltage holding transistor 22 in a non-conductive state decreases and transistor 22 starts to again become conductive. This initiates the regenerative cycle which results in the rapid turn on of transistor 22 and turn off of transistor 22 as well as the subsequent rapid turn off" of transistor 22 and turn on of transistor 30.

It can be seen that when transistor 30 is in a conductive state, the emitter-base 44, 40, circuit of load or power transistor 42 is biased into conduction thereby completing the circuit through the emitter 44 and coliector 46 thereof causing energization of the load 50 comprised of parallel loads 54, 56 and 58. As should be apparent from the preceding, power or load transistor 42 is made conductive during the period that multivibrator transistor 30 is conductive. Therefore, when transistor 30 is cyclically rendered non-conductive, as previously described, power transistor 42 is also rendered non-conductive causing the load circuit to be opened as between load circuit conductor portions 45 and 48.

For purposes of discussion, load 50 may be considered as comprising, for example, a plurality of lamps 54 and 56 situated so as to be visible externally of a vehicle while load 58 may represent a relatively small indicator lamp carried within the vehicle so as to be visible to the vehicle operator.

Accordingly, with the above assumptions, it can be see that whenever transistor 30 is cyclically made inductive, the power or load transistor 42 is likewise turned on thereby completing the circuit through the load circuit, comprised of conductors 45, 48 and 52, and load 50 causing the externally situated lamps 54 and 56 to be energized, creating an external signal, and indicator lamp 58 to be simultaneously energized creating an internal indicator signal for the operator.

As can be seen, resistor 98 is in parallel with the power transistor 42 and, therefore, combines with the load 50 to in effect form a voltage divider. For purposes of illustration, let it be assumed that resistor 98 has a resistance value comparatively very high to that of load 50 and that its resistance value is in the order of nine times the effective resistance value of load 50. Therefore, whenever transistors 30 and 42 are off, 9/10 of the voltage drop occurs across resistor 98 while 1/10 of the total voltage drop, across conductors 10 and 12, occurs across the load 50. However, it should be remembered that the effective resistance of load 50 is determined by the following:

where:

R, effective resistance;

R resistance of load 58;

R resistance of load 56; and

R resistance of load 54.

Now let it be assumed that for some reason one of the external loads or lamps, such as, for example, lamp 54, has become burned-out thereby in effect causing such lamp 54 to appear as an electrically open branch circuit. Consequently, the effective resistance of load 50 will now increase because the effective resistance will be determined by the following:

where:

R, new effective resistance;

R, same unchanged resistance of load 58; and

R same unchanged resistance of load 56. t For purposes of illustration, let it be assumed that R, is now of a value twice that of original effective resistance R With this assumption, it then becomes apparent that with, for example, lamp 54 being burned-out whenever transistors 30 and 42 are off 9/ ll of the voltage drop will occur across resistor 98 while 2/11 of the total voltage drop will occur across the load 50, which is now comprised of lamps 56 and 58.

Accordingly, in view of the above, it can be seen that with load transistor 42 in its off or non-conductive state and with the occurrence of an outage in the total load 50, the resulting increase in voltage drop across the load 50 and transistor base-emitter divide, due to the outage, is sufficient to cause transistor 80 to become conductive thereby completing a cycle time modifying circuit from point 74 through conductor 90, resistor 88, collector 86, emitter 82, conductors 84 and 12 to ground at 20.

The effect of such a cycle time modifying circuit will be better appreciated when the circuit described by resistor 26, capacitor 72, resistor 70 and conductor 12 joining resistors 70 and 72 is first considered. From previous description, it should be apparent that capacitor 72 had been fully charged at the moment that transistor 22 was turned on and transistor 30 was turned off." At the moment that transistor 30 was turned off" capacitor 72 starts to discharge generally in the loop defined by resistors 70, 26 and conductor 12 therebetween and in so doing reverse biases transistor 30 so as to keep it in its off condition. Obviously, in view of the above, the length of time that transistor 30 will be held off is dependent on the length of time required to sufficiently discharge capacitor 72 which, in turn, is primarily dependent on the value of resistor 70.

Therefore, whenever the cycle time modifying circuit is completed, as described above, resistor 70 is effectively placed in parallel with resistor 88 which results in an effective resistance value less than the resistance value of either resistor 70 or 88. The lowering of the resistance value reduces the time required to sufficiently discharge capacitor 72 and, therefore, reduces the off time portion of the overall operating cycle of transistor 30.

This is graphically illustrated in FIG. 2 by the comparative curves 120 and 122 with curve 120 representing a normal operation without outage and curve 122 representing operation of the flasher circuitry with an outage. If, in curve 120, portions 124 and 126 represent the on times while portions 128 and 130 represent the of times of transistor 30 and if, in curve 122, portions 132, 136 and 140 represent the on times while portions 134, 138 and 142 represent the of times of transistor 30, it can be seen by comparison that the on time of transistor 30 remains the same whether or not an outage exists in the overall load 50 while the off time of transistor 30 is reduced whenever an outage is present.

Accordingly, in view of the preceding, it should be apparent that the invention herein disclosed and described provides means for producing a timed signal to load switching means, in order to cause said load switching means to become cyclically closed and opened, and additional means sensitive to the occurrence of an outage in the load for varying the cycle time of the means for producing a timed signal in order to thereby produce a switching rate indicative of an abnormal load condition. Various other embodiments and modifications of the invention are of course possible and FIGS. 3 and 4 hereof illustrates only two of such modifications. In both FIGS. 3 and 4 only so much of the circuit of FIG. 1 is repeated as is considered sufficient to disclose the modification. All elements in FIGS. 3 and 4 which are like or similar to those of FIG. 1 are identified with like reference numbers.

Referring to FIG. 3, it can be seen that a zener diode 102 is provided in circuit with conductor 94 and resistor 95. As is known, a zener diode will maintain a substantively constant voltage once its break-down voltage attained. Accordingly, the effect of providing zener 102 is to require the occurrence of some predetermined higher value of voltage drop to occur across the load 50 before transistor 80 will be permitted to become conductive in the manner previously described. This may be especially of value in situations where the voltage drop across the normal load is close to the value required to cause transistor to become conductive and both operating and ambient temperatures may be such as to at times cause transistor 80 to conduct even when there is no outage.

Another arrangement for accomplishing the same result is illustrated in FIG. 4 wherein diodes 112 and 114 are situated in series in the emitter circuit. The use of such diodes (one or more in series) also required the attainment of a higher voltage to be impressed across the base-emitter diode of transistor 80 as well as the diodes 112, 114 before transistor 80 becomes conductive.

In view of the preceding, it should be apparent that functional equivalents could be substituted for the various sections of the circuitry as well as components or elements contained therein. Also, as should be apparent, the circuitry disclosed could be practiced employing N-P-N transistors for those that are shown as P-N-P and vice versa where appropriate polarity changes are made as is well known in the art.

Although only three embodiments of the invention have been disclosed and described, it should be apparent that other embodiments and modifications of the invention are possible within the scope of the appended claims.

We claim:

1. In a flasher circuit of the type adapted to intermittently energize a load from a voltage source and including means for producing intermittent control signal impulses, and a switching device having its output connected between the load and the voltage source and having its input connected with said means and adapted to be switched between on and off conditions in response to said control signal impulses to connect and disconnect the load and the voltage source, said load comprising plural signal lamps connected in parallel directly across the voltage source whereby the entire voltage of the source is applied to the load when the switching device is on, the improvement comprising a resistor connected across the output of said switching device and in series with the load whereby the resistor and load constitute a voltage divider across the voltage source when the switch is off, the voltage across the load during the interval when the switching device is off being less than a predetermined value when all of the plural signal lamps are operative and being greater than the predetermined value when one of said signal lamps is open circuited, and control means having an input connected with the junction of the load and the resistor and being responsive to the voltage across a portion of said voltage divider for producing an output when the voltage across the load is greater than said predetermined value, thereby being indicative of an open circuit condition of one of said lamps.

2. The invention as defined in claim 1 wherein said control means has its input connected across said load and includes a voltage threshold device adapted to become conductive at said predetermined voltage.

3. The invention as defined in claim 1 wherein said control means is operatively coupled to the input of said switching device to change the action thereof upon the occurrence of an open circuit condition of one of said signal lamps.

4. The invention as defined in claim wherein said switching device is a power transistor and said control means comprises a control transistor having its input connected across said load.

multivibrator comprises a pair of resistance capacitance cross-coupling networks connected respectively with said first and second transistors for controlling the conductive interval thereof, said control transistor having its output connected to one of said networks whereby the conductive interval of one of the transistors in the multivibrator is changed when the control transistor changes from one conductive condition to another in response to an increase of load voltage during the nonconductive interval of the power transistor. 4:

STATES @FFIICE I @E'MMQA'EE w esssmis Patent No. 3'735'196 Dated y'22,1973

Inventor) John F. Bolinger; Wilhelm K. Kolseer, deceased It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 50, "22" should be 30--.

Col.4, lines 8-9, "inductive" should be --conductive.

Col. 5, line 51, "illustrates" should be --illustrate--.

Col. 6 line 64, after "claim" insert l---.

Signed and sealed this 25th day of December 1973,,

(SEAL) & ttest:

EDWARD M.F.T ETCHER,JR. RENE Do TEGTMEYER Attesting Officer Acting Commissioner of Patents mm po-wso (10-69) v uscoMM-oc 60376-P69 fl U.S. GOVERNMENT PRINTING OFFICE: I969 0-666-33 I 

1. In a flasher circuit of the type adapted to intermittently energize a load from a voltage source and including means for producing intermittent control signal impulses, and a switching device having its output connected between the load and the voltage source and having its input connected with said means and adapted to be switched between on and off conditions in response to said control signal impulses to connect and disconnect the load and the voltage source, said load comprising plural signal lamps connected in parallel directly across the voltage source whereby the entire voltage of the source is appLied to the load when the switching device is on, the improvement comprising a resistor connected across the output of said switching device and in series with the load whereby the resistor and load constitute a voltage divider across the voltage source when the switch is off, the voltage across the load during the interval when the switching device is off being less than a predetermined value when all of the plural signal lamps are operative and being greater than the predetermined value when one of said signal lamps is open circuited, and control means having an input connected with the junction of the load and the resistor and being responsive to the voltage across a portion of said voltage divider for producing an output when the voltage across the load is greater than said predetermined value, thereby being indicative of an open circuit condition of one of said lamps.
 2. The invention as defined in claim 1 wherein said control means has its input connected across said load and includes a voltage threshold device adapted to become conductive at said predetermined voltage.
 3. The invention as defined in claim 1 wherein said control means is operatively coupled to the input of said switching device to change the action thereof upon the occurrence of an open circuit condition of one of said signal lamps.
 4. The invention as defined in claim wherein said switching device is a power transistor and said control means comprises a control transistor having its input connected across said load.
 5. The invention as defined in claim 1 wherein said means for producing intermittent control signal impulses is a multivibrator including first and second cross-coupled transistors and wherein said switching device is a power transistor having its input operatively connected with the second transistor of the multivibrator and having its output connected with said load across the voltage source, said control means comprising a control transistor having its input connected across said load.
 6. The invention as defined in claim 5 wherein said multivibrator comprises a pair of resistance capacitance cross-coupling networks connected respectively with said first and second transistors for controlling the conductive interval thereof, said control transistor having its output connected to one of said networks whereby the conductive interval of one of the transistors in the multivibrator is changed when the control transistor changes from one conductive condition to another in response to an increase of load voltage during the nonconductive interval of the power transistor. 